In a raster graphics system, an image is created by an array of points, known as pixels, illuminated to different intensities. In a monochrome system, this intensity is known as luminance. In a color graphics system, there are separate luminances for red, green, and blue. Thus, a color graphics system can be considered to be three monochrome graphics systems operating in parallel.
Typically, objects in such a system are modeled as a series of polygons, where each vertex of the polygon may be at a different luminance. The points on the interior of the polygon will have luminance values interpolated from the luminance values at the vertices. As is schematically illustrated in FIG. 1, in the past, the luminance for each pixel has been calculated individually by computing the distance from each pixel to each of the vertices of the polygon and doing a linear interpolation. This type of linear shading is commonly known as "Gouraud" shading. Because of the extreme computational load, this process is very slow. The invention offers a method to rapidly draw linearly shaded polygons in a raster graphics system, thus, alleviating the aforementioned deficiencies of the prior art.